1. Field of the Invention
The present invention relates to apparatus having a service of radiation, an optical system for projecting the radiation on at least one radiation-sensitive detector via an information carrier. It relates more particularly to an A/D converter control circuit constructed to convert an analog signal proportional to the detected radiation intensity into a digital signal which controls the radiation intensity.
2. Description of the Related Art
Apparatus of this type is disclosed in European Patent Application EP-A-0,138,273. This known apparatus employs a number of photo-sensitive semiconductors to convert the light reflected from the information carrier into a corresponding number of analog information signals. These information signals are applied to an A/D converter via a multiplexer, which converter supplies a corresponding number of digital output signals to a processing circuit. This processing circuit supplies a digital data signal, which signal is representative of the information recorded on the optical record carrier, and also supplies control signals for positioning and focus control of the optical system.
In this prior-art apparatus problems may arise if the input signal range of the converter is not adapted to an optimum extent to the conversion range of the converter. If the photo-sensitive semiconductor which converts the light reflected from the information carrier into an analog signal supplies signals whose amplitude exceeds the maximum amplitude which can be handled by the A/D converter, the bit sequence supplied by the A/D converter will not be a correct representation of the analog input signal. Conversely, if the analog signals supplied by the photo-sensitive semiconductor vary within an input signal range smaller than the conversion range of the A/D converter, this conversion range is not utilized to the full extent so that the analog input signals are digitized with a resolution smaller than attainable with A/D converter.